1. Field of the Invention
The present invention relates to a master cylinder with an annular seal member retained by an annular seal retainer for restricting at least axial movement of the seal member in response to a movement of a master piston. Also, the invention relates to the seal retainer for use in the master cylinder, and relates to a method for installing the seal retainer in the master cylinder.
2. Description of the Related Arts
Heretofore, there are known various kinds of master cylinders for supplying hydraulic braking pressure into wheel brake cylinders, as disclosed in Japanese Utility-model Publication No.2554584, for example. In this publication, there is disclosed such a master cylinder that includes a primary piston and a secondary piston accommodated in a cylinder bore, and proposed is an improvement in a structure for preventing the secondary piston from moving toward the primary piston by more than a predetermined distance due to variation of pressure in the first hydraulic chamber and second hydraulic chamber. In the publication, there are disclosed a primary cup and a secondary cup having an approximately C-shaped cross section, respectively, and cup support members (42 and 43 in FIG. 1 of the publication) for preventing those cups from moving in response to the movement of the piston.
According to the master cylinder as disclosed in the publication, a guide member and a cover are placed at a rear end portion of a cylinder (housing) to constitute a part of the cylinder, so as to support the secondary piston. As apparent from this structure of the master cylinder, the rear end portion of the cylinder is formed with stepped bores whose inner diameters are gradually enlarged rearward (toward a brake pedal), and into which the cup support member for restricting the movement of a cup-like seal member, the seal member, a guide member and the cover are assembled in sequence. Although the number of parts is large and the assembling time is long according to the master cylinder as described above, it was impossible in effect to insert an annular cup support member from the cylinder bore having a smaller diameter than the diameter of the cup support member. Therefore, any particular effort has not been given to produce a master cylinder having a different structure from that of the master cylinder as described above. As a result, the master cylinder has been produced at a relatively high cost.
In view of those backgrounds in this technical field, supposing that the seal retainer could be inserted into the cylinder bore in such a state that the seal retainer is reduced in diameter in advance, then the seal retainer could be received in a groove formed in the cylinder bore to hold the seal retainer, and then enlarged in diameter, not only the reduction of the number of parts could be achieved, but also a large amount of reduction in assembling time could be made.